Genetic tests for cancer susceptibility have the potential to reduce cancer mortality by targeting intensive cancer risk reduction interventions to high risk individuals. Testing for mutations in the breast cancer susceptibility genes, BRCA1and BRCA2, is one of the earliest examples of cancer genetic susceptibility testing to become incorporated into clinical practice and be linked to multiple evidence based options for cancer risk reduction. Although recommendations for consideration of BRCA1/2 testing among high risk groups have existed for nearly ten years, evidence suggests that testing uptake has been limited and that substantial racial disparities in testing utilization may exist. Understanding the underlying causes of these disparities is critical for the development of strategies to ensure that advances in genomics are translated into equitable improvements in clinical care. The determinants of utilization of genetic testing are complex and encompass patient, provider and system factors. Although racial disparities in health care have traditionally been traced to differences in patient characteristics or physician bias, a growing body of literature indicates that differences in providers across patient racial groups are an important and often fundamental of health care disparities. Whether the sorting of patients of different races across different providers is an important determinant of racial differences in the use of genetic or genomic technologies is currently not known. In this proposal, we outline a population based, prospective cohort study that will determine the rates of BRCA1/2 testing among Black and White women with early onset breast cancer and investigate the relative contribution of individual patient characteristics ("within provider effects") vs. provider characteristics ("between provider effects") to racial differences in utilization. We will use both multi-level models to examine the contribution of specific patient and provider characteristics and conditional logistic regression and decompositional techniques to determine the relative proportion of the racial difference in testing explained at the patient vs. the provider level. Building on our prior work in this area, we will test specific hypotheses about the contribution of health care related distrust and insurance coverage at the patient level and specific hypotheses about the contribution of attitudes towards innovation and access to resources at the provider level. We will compare these results to the contribution of the same factors to other known racial disparities in breast cancer management, asking whether the patient and provider characteristics that lead to disparities in BRCA1/2 testing also lead to disparities in use of adjuvant therapy and whether a provider's performance on one outcome also predicts their performance on the other outcomes. Public Health Relevance: Genetic susceptibility tests have the potential to reduce cancer mortality by targeting intensive cancer risk reduction interventions to high risk individuals. BRCA1/2 testing is one of the earliest examples of cancer genetic susceptibility testing to become incorporated into clinical practice and be linked to multiple evidence based options for cancer risk reduction. This project will increase our understanding of the use of testing among Black and White women with early onset breast cancer and the patient and provider determinants of disparities in that use.